The present invention relates to a coordinate measuring machine with a measuring system for measuring a workpiece, a carrier structure for carrying the measuring system, and a base plate for supporting the workpiece, wherein the carrier structure is movably guided at least in one direction on the base plate, and wherein the coordinate measuring machine also has a first support system with at least three supports for supporting the base plate.
The present invention also relates to a method for compensating for large workpiece masses on a coordinate measuring machine.
A coordinate measuring machine is for example shown in document DE 102 29 823 A1.
Coordinate measuring machines are generally known in the prior art. They serve the purpose of determining coordinates of workpieces with high precision. In this way, for example, individual points, point paths, dimensions and/or forms of the workpiece can be determined or checked with high precision. Such coordinate measuring machines are used for example in quality assurance or in areas of activity such as “reverse engineering”.
In the case of coordinate measuring machines, a measuring system, for example a measuring system operating on a tactile and/or optical basis, is coupled to a carrier structure, which makes it possible for the measuring system to be moved and aligned within a measuring space. Very many different types of carrier structures are known in principle, for example gantry constructions, horizontal-arm systems, table measuring devices and all other types of robot-assisted measuring systems, to name just a few examples. The carrier structure is in this case generally arranged on a base plate, in relation to which the carrier structure is relatively movable. Then, the workpiece to be measured is also arranged on the base plate.
The high-precision measuring requirements require a horizontal alignment of the base plate and retention of this alignment during a measuring operation. This means not only a possible damping of vibrations occurring, but also compensation for changing forces of weight applied to the base plate. Such changing of the forces of weight applied may be caused for example by placing on a workpiece or else by moving the carrier structure in relation to the base plate.
The document DE 38 088 71 A1 proposes a coordinate measuring machine that is produced in a welded-steel construction and has a compact base frame with welded-in and hardened guides and also a measuring table plate welded into the base frame. The entire base frame is intended to rest on a total of four air spring elements.
A dynamic inclination correction has also been proposed for coordinate measuring machines, in the form of a method for determining at least one coordinate of a structure in the measuring volume of a coordinate measuring machine mounted on supports with variable inclination, which comprises the steps of determining a measured value for the at least one coordinate, determining a value for the inclination of the coordinate measuring machine and correcting the measured value for the at least one coordinate in dependence on the determined value for the inclination of the coordinate measuring machine. By controlling the supports, formed as air springs, in a control circuit, it is intended that an inclination of the coordinate measuring machine is reduced.
Nowadays, support systems for coordinate measuring machines are generally designed as a three-point bearing system or reduced four-point bearing system with three or four air spring elements. The base plates are in most cases made of granite. For example, coordinate measuring machines of a gantry construction may nowadays be designed with large dimensions, which also makes the measuring of large workpieces possible. Large dimensions of the workpieces are also accompanied by correspondingly high masses and weight forces, which may well lie in the range of one to several tonnes. If at least one guide for the carrier structure of the measuring system is provided directly on the base plate, undesired measuring deviations may occur when measuring such workpieces with high masses and consequently resultant high weight forces on the base plate.
It is therefore an object of the present invention to provide a coordinate system that has an improved support system.